Key Financial Data Of Group
| Concept | 2023-04-01 to 2023-09-30 | As at 2023-09-30 | 2023-07-01 to 2023-09-30 | As at 2023-03-31 | 2022-04-01 to 2023-03-31 | 2022-04-01 to 2022-09-30 | As at 2022-09-30 | 2022-07-01 to 2022-09-30 | 
|---|---|---|---|---|---|---|---|---|
| Key financial data of group | ||||||||
| Business results of group | ||||||||
| Ordinary profit (loss) | 
                                                236,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                1,074,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                387,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
| Net assets | — | 
                                                11,004,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                10,951,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                10,576,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Total assets | — | 
                                                18,443,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                18,354,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                17,694,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
| Basic earnings (loss) per share | 
                                                12.48
                                                
                                             | — | 
                                                9.63
                                                
                                             | — | 
                                                59.10
                                                
                                             | 
                                                20.93
                                                
                                             | — | 
                                                17.67
                                                
                                             | 
| Diluted earnings per share |  | — | — | — |  |  | — | — | 
| Equity-to-asset ratio | — | 
                                                0.597
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
                                                0.597
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | — | 
                                                0.598
                                                
                                                    
                                                        xbrli:pure
                                                    
                                                
                                             | — | 
| Net cash provided by (used in) operating activities | 
                                                358,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                1,067,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -836,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
| Net cash provided by (used in) investing activities | 
                                                -39,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                -48,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -58,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
| Net cash provided by (used in) financing activities | 
                                                -222,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                -358,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -177,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
| Cash and cash equivalents | — | 
                                                5,579,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                5,482,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                3,750,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — |